El Nino, Global Warming, and Anomalous U.S. Winter Warmth

It has now become all too common. Peculiar weather precipitates immediate blame on global warming by some, and equally immediate pronouncements by others (curiously, quite often the National Oceanic and Atmospheric Administration in recent years) that global warming can’t possibly be to blame. The reality, as we’ve often remarked here before, is that absolute statements of neither sort are scientifically defensible. Meteorological anomalies cannot be purely attributed to deterministic factors, let alone any one specific such factor (e.g. either global warming or a hypothetical long-term climate oscillation).

Lets consider the latest such example. In an odd repeat of last year (the ‘groundhog day’ analogy growing ever more appropriate), we find ourselves well into the meteorological Northern Hemisphere winter (Dec-Feb) with little evidence over large parts of the country (most noteably the eastern and central U.S.) that it ever really began. Unsurprisingly, numerous news stories have popped up asking whether global warming might be to blame. Almost as if on cue, representatives from NOAA’s National Weather Service have been dispatched to tell us that the event e.g. “has absolutely nothing to do with global warming”, but instead is entirely due to the impact of the current El Nino event.

[Update 1/9/07: NOAA coincidentally has announced today that 2006 was officially the warmest year on record for the U.S.]
[Update 2/11/08: It got bumped to second place. ]

So what’s really going on? The pattern so far this winter (admittedly after only 1 month) looks (figure on the immediate right) like a stronger version of what was observed last winter (figure to the far right–note that these anomalies reflect differences relative to a relatively warm 1971-2000 base period, this tends to decrease the amplitude of positive anomalies relative to the more commonly used, cooler 1961-1990 base period). This poses the first obvious conundrum for the pure “El Nino” attribution of the current warmth: since we were actually in a (weak) La Nina (i.e., the opposite of ‘El Nino’) last winter, how is it that we can explain away the anomalous winter U.S. warmth so far this winter by ‘El Nino’ when anomalous winter warmth last year occured in its absence?

The second conundrum with this explanation is that, while El Nino typically does perturb the winter Northern Hemisphere jet stream in a way that favors anomalous warmth over much of the northern half of the U.S., the typical amplitude of the warming (see Figure below right) is about 1C (i.e., about 2F). The current anomaly is roughly five times as large as this. One therefore cannot sensibly argue that the current U.S. winter temperature anomalies are attributed entirely to the current moderate El Nino event.

Indeed, though the current pattern of winter U.S. warmth looks much more like the pattern predicted by climate models as a response to anthropogenic forcing (see Figure below left) than the typical ‘El Nino’ pattern, neither can one attribute this warmth to anthropogenic forcing. As we are fond of reminding our readers, one cannot attribute a specific meteorological event, an anomalous season, or even (as seems may be the case here, depending on the next 2 months) two anomalous seasons in a row, to climate change. Moreover, not even the most extreme scenario for the next century predicts temperature changes over North America as large as the anomalies witnessed this past month. But one can argue that the pattern of anomalous winter warmth seen last year, and so far this year, is in the direction of what the models predict.

In reality, the individual roles of deterministic factors such as El Nino, anthropogenic climate change, and of purely random factors (i.e. “weather”) in the pattern observed thusfar this winter cannot even in principle be ascertained. What we do know, however, is that both anthropogenic climate change and El Nino favor, in a statistical sense, warmer winters over large parts of the U.S. When these factors act constructively, as is the case this winter, warmer temperatures are certainly more likely. Both factors also favor warmer global mean surface temperatures (the warming is one or two tenths of a degree C for a moderate to strong El Nino). It is precisely for this reason that some scientists are already concluding, with some justification, that 2007 stands a good chance of being the warmest year on record for the globe.

A few other issues are worthy of comment in the context of this discussion. A canard that has already been trotted out by climate change contrarians (and unfortunately parroted uncritically in some media reports) holds that weather in certain parts of the U.S. (e.g. blizzards and avalanches in Colorado) negates the observation of anomalous winter warmth. This argument is disingenuous at best. As clearly evident from the figure shown above, temperatures for the first month of this winter have been above normal across the United States (with the only exceptions being a couple small cold patches along the U.S./Mexico border). The large snowfall events in Boulder were not associated with cold temperatures, but instead with especially moisture-laden air masses passing through the region. If temperatures are at or below freezing (which is true even during this warmer-than-average winter in Colorado), that moisture will precipitate as snow, not rain. Indeed, snowfall is often predicted to increase in many regions in response to anthropogenic climate change, since warmer air, all other things being equal, holds more moisture, and therefore, the potential for greater amounts of precipitation whatever form that precipitation takes.

Another issue here involves the precise role of El Nino in climate change. El Nino has a profound influence on disparate regional weather phenomena. Witness for example the dramatic decrease in Atlantic tropical cyclones this most recent season relative to the previous one. This decrease can be attributed to the El Nino that developed over the crucial autumn season, which favored a strengthening of the upper level westerlies over the tropical North Atlantic, increased tropical Atlantic wind shear, and a consequently less favorable environment for tropical cyclogenesis.

If a particular seasonal anomaly appears to be related to El Nino, can we conclude that climate change played no role at all? Obviously not. It is possible, in fact probable, that climate change is actually influencing El Nino (e.g. favoring more frequent and larger El Nino events), although just how much is still very much an issue of active scientific debate. One of the key remaining puzzles in the science of climate change therefore involves figuring out just how El Nino itself might change in the future, a topic we’re certain to discuss here again in the future.

As we are fond of reminding our readers, one cannot attribute a specific meteorological event, an anomalous season, or even […] two anomalous seasons in a row, to climate change.

It seems to me that an “anomalous” some number of seasons in a row is the definition of “climate change.”

How many anomalous seasons in a row must we have before we can say that what was once anomalous is now normal, and “the climate has changed”?

[Response: Your point is well taken, and raises one of the trickier issues. Lets extend the dice rolling analogy we used in our Hurricane and Global Warming” article of last year. Lets characterize the two anomalously warm U.S. winters in a row, last year and this year (assuming the rest of January and February are not anomalously cold) as ‘snake eyes’ (double “1”s coming up in a roll of two dice, for the non-gamblers among us). Well, snake eyes will come up 1/6*1/6 = one out of every 36 rolls of two independent dice (3% of the time), randomly. Suppose we load the dice e.g. by erasing the “twos” and replacing them with “ones”. Snake eyes will now come up 1/3*1/3 = one out of every nine rolls of the two dice (11% of the time). It may take us quite a few rolls of the dice to determine decisively that the dice have been loaded (i.e. to conclude that the percentage is statistically significantly higher than the expected 3% rate). On the other hand, suppose that you really loaded the dice, by erasing the “twos”, “threes”, “fours” and “fives” and replacing them all with “ones”. Then snake eyes will come up 5/6*5/6 = 25/36, i.e. approx 70% of the time, rather than the expected 3% of the time. In this case, we would figure out quite quickly that the dice were loaded. So depending on just how loaded the dice really are, we may have to continue rolling for some time to determine decisively that they are loaded with respect to any particular phenomenon (e.g. U.S. winter warmth). On the other hand, such information does not exist in isolation. We have many other independent (theoretical and empirical) lines of evidence of climate change. The totality of the evidence convinces the vast majority of scientists in the field that we are indeed already seeing the influence of climate change in the collective observable phenomena. -mike]

One reason to be cautious about using “average” in talking to the general public or to a scientific/technical audience is its ambiguity. Depending on the context, “average” may refer to the arithmetic mean, the median, the geometric mean, or the harmonic mean. Each of these is appropriate in certain contexts and one of the ways of lying with statistics is to use an inappropriate one and refer to it, correctly, as the average whatever.

For instance, you might tell us that average real income in the US has gone up in the last 6 years, referring to the arithmetic mean, even though median real income has decreased.

“Normal” is probably a good surrogate for “within the normal range of variation” and doesn’t need to refer to the Gaussian distribution. It would probably be better to use the whole phrase or give a 5/95 range.

That the term ‘climate normal’ has been curtailed to ‘normal’ is perhaps to be regretted, but most people hereabouts know exactly what ‘normal’ means, as I hazard do people hereabouts who wish to pretend mischievously is otherwise the case.

According to the WMO definition, climate average/mean/normal are interchangeable/synonymous terms. It is an arithmetic calculation based on observed climate values for a given location over a specified time period (‘normally’ 30 years) and is used to describe the climatic characteristics of that location. Real-time values, e.g. daily temperature, are compared with the ‘climate normal’ to determine how unusual or how great the departure from ‘average’ they are (whether you’re talking climatology or meteorology — and it is certainly the latter case recently here).

Since this is a blog, not a peer-reviewed journal, I see no real problem with using ‘normal’. And anyone under a misapprehension as to what ‘normal’ means is likely to be corrected sharpish and/or pointed in the direction of the resources connected to this site.

As to how this ‘normal’ term is portrayed in the media, that is in the domain of reporters and editors and their critically thinking (or otherwise) readers.

I am new to this stuff so please excuse the naivete of this question, but when we say the “warmest year on record” do we mean historical record, or since the mid 1800’s when regular measurements of air temperature were started?

[Response: Depending on how much the trust the earlier instrumental records, and what you’re willing to consider ‘global’ coverage, we have a reasonably reliable record back to the mid 19th century. So by ‘warmest on record’ I simply mean in the context of the instrumental record available back to the mid 19th century. As for extending the record even further back than this using more tentative proxy and/or early instrumental and historical data, there is much discussion of this on the site. Just go to the ‘paleoclimate’ section of our ‘archive’. -mike]

Mike – – Regarding this discussion of climate normals, I wanted to ask you to post a few time series of climate normals if you could. Most people have a sense of what a 30-yr climate normal is. I think a simple plot showing how the “preceived normal” has changed over time would be interesting and compelling. I imagine that you or your RC colleagues would have the data at your fingertips to plot the 1930-1960, 1940-1970, 1950-1980 . . . . . 1970-2000 surafce air temperature normals for a few representative stations. These plots would how perceptions of what is “normal” are changing in different areas. Perhaps this has already been done and you could suggest a link.

[Response: Thanks, this would be useful. But unfortunately I don’t have the data at my fingertips. We’re so used to working with anomalies that we usually just discard the climatologies. Perhaps some RC followers know of an online resource that provides a comparison of the evolving climatologies for one or more observing stations? -mike]

Regarding the connection between El Nino conditions and greenhouse gas (GHG) concentrations, I would be interested in RC’s opinion on the explanation for the apparently high temperatures in the Pliocene (5 to 3 million years ago (MYA)). At that time the GHG concentrations were not much above today’s level, yet sea levels were 10 to 20 meters higher.

Two competing hypotheses both seem to involve alterations of ocean currents and ocean surface temperatures. The earlier hypothesis was that the restrictions of the Indonesian and Panamanian seaways were responsible for the shift to major northern hemisphere glaciations starting about 2.75 MYA. The other posited by A.C. Revelo and others at U.C. Santa Cruz and Mitchell Lyle at Boise State U. (see http://www.sciencemag.org/cgi/content/full/309/5735/758 and Nature Magazine, May 20, 2004, Vol. 429, pp. 263-267) is that higher temperatures might induce a permanent El Nino which could cause a significant positive feedback and amplify global warming. These two hypotheses have hugely different implications for the sea level rise in the centuries ahead, even if CO2 concentrations do not exceed 450 ppm.

Even if the El Nino feedback is only a partial reason for the high sea level in the Pliocene, that would have significant implications for long-term planning for coastal areas. Which of these two hypotheses is more credible? Are there other hypotheses?

Ahem … So what was the need to pretend that I was talking nonsense in the previous thread and then turning around to make the same point (re: wrong order of magnitude) here?

[Response: Sometimes our readers do raise points worthy of greater discussion in a more appropriate thread. So a hat tip to you indeed Sashka. You got a brief response earlier, and an expanded one in this latest post. -mike]

RE: #58 – In the day (old fart that I am) the “earlier hypothesis” was how they taught it in the UC Santa Barbara Geological Sciences Dept.

I seem to recall an earlier thread where I brought it up, I seem to recall Dano and others making quite and effort to discredit it. IIRC – the discrediting factor was the time lag between the tectonic closures you mentioned, and the onset of the Pleistocene. My own continuing curiousity about it is based on my studies and work with transients in semi chaotic networks. An event (a step funtion or unit impulse) may occur, then it may take some time before the resulting perturbation settles and a new astable condition sets up. The tectonic closures would have constituted a fairly serious transient being imparted to ocean current systems. It would have taken some time after them for the new ocean current regime to be properly set up (the current THC/global conveyer system, more or less). Personally I would not rule out this theory. The time lag is actually expected. That’s how networks behave.

It’s just as well that single events or seasons cannot conclusively be attributed to GW.

What’s important is the recognition that AGW (assuming we keep emitting GHGs) will on the whole include greater warming, heat deaths, perhaps greater droughts, floods, storms, glacier melt, crop harm, fish harm (from warming, current disruption, acidification), wildlife harm, and many other problems. Because what we need to do is work to reverse this and avoid these future harms on the whole — rather than get tied up in court for decades trying to sue the pants off the perpetrators of some wacky weather event in Idaho. We need action to avoid enhancement of future hurricanes, not endless debates and recriminations about Katrina 2005 that prevent us from doing anything constructive to mitigate future GW. (I was able to tell a friend, a victim of Hurricane Rita, that it was in part to avert such mega-hurricanes, that I have been reducing my GHGs since 1990).

I was actually motived to start reducing because GW “may have been exascerbating” drought & death in Africa. “May have” was a high enough standard to motivate me & it wasn’t unit 1995 that the 1st scientific studies reached 95% certainty re AGW. Likewise wacky weather and other possible current effects of GW (that portent worse to come in the future) should be good motivators for others…not to change weather tomorrow in some tiny location, but to avert or reduce such problems or increased effects in the future around the world. I hope no one realistically thinks that by running multiple instead of single errands or turning off the motor in drive-thrus that will make it colder today in Cincinnati so Johnny can build a snowman.

Not to rain on anyone’s (warm) parade, but down here we’ve just had the coldest December for 60 years, and icebergs off the coast. Unsurprisingly, our local sceptics reckon this disproves global warming. For my part, I will acknowledge the variability in the system – but not revel in it. Could I please have some of your anomalous warmth for my grapevines?

On attributing single weather events to climate change: has nobody really tried to formalize this?

For example, suppose you have a background model M1, giving density p(x|M1) for a quantity, say temperature. M1 could represent a stable climate, and be for example a gaussian or t-distribution derived from past records. An alternative model M2, that could be derived from a climate model with AGW taken into account, predicts another density p(x|M2) for the same quantity.

The basic idea would then be to quantify the surpriseness of an observation under both models, and compare these to some base level.

By decision theory one can maybe justify the rationality of log-probability as a measure of surprise – at least log-probabilities are justifiable as a “score function”. Now if the most probable event by M1 is x_0, one can use it as a baseline, and evaluate the “surpriseness” of event x_1 under model M1 as log p(x_0|M1) – log p(x_1|M1). Under the model M2 the event x_1 would (maybe) be less surprising, and that surprise could be measured by log p(x_0|M1) – log p(x_1|M2). The numbers are comparable, and ratios of log-odds would allow fractional attribution of surprise. (No problem with using densities here as long as a physical symmetry spans a reasonable unique (Lebesque) measure into the x-space. But getting a justifiable baseline for the log-odds is critical and might be a challenge.)

Of course the result would be conditional on a climatology and a climate model, and the climately model must be able to generate probability distributions for single events, such as daily temperatures on a station. This, especially the latter, adds a lot of assumptions. Model uncertainty, on the other hand, is easy to include if it’s quantifiable, once one gets the basic framework right.

My version above is just hand-waving, and would probably fail miserably under a closer look. But has anyone seriously tried something along these lines and been unsuccessful?

[Response:Good question. I’m not sure if I’ll succeed giving a sensible answer, but I’ll try: Your ideas bear many similarities to Bayesian statistics and attribution studies, e,g, Leroy (1998). Although this kind of analysis gives a probability associated with one explanatory factor, it cannot prove that the causation unless the probability is 0 or 1 (which is rarely the case). Furthermore, in complex systems such as the climate, it is difficult/impossible to statistically make any definete link between only one given event and a climate change, as the latter implies a change in the statistics – the pattern of behaviour (take the anology of a loaded dice). -rasmus]

An amateurs observations:
There is a bug in the NAO index! Some surfers in the NW parts of Norway were excited when they learned about the NAO index. The index will normally show the track of low pressure systems in the N Atlantic. High index should indicate lows coming from the south tip of Greenland and crash right into the NW coast of Norway producing enjoyable waves. The peak in the NAO was in 90-92, when several hurricanes struck the coast. For the last three months, something odd has happened. The index has been quite positive, storms have been frequent, but the lows are traveling far more towards north, giving mild southernly winds in norway (and record high temperatures). Today is the very first day in many months with lows coming from north.
I wonder why the lows are coming from SW, not W / NW as usual.
To me, AGW is not a direct explanation. How well do we understand why the weather systems are stuck in these “modes”?

Chicago experience: Christmas Eve, 1984, 70 F. Christmas Eve, 1985, -24 F. A 94 F degree difference on the same day in the same location, one year later (admittedly one was a high and one was a low, but the high in 1985 was still very cold).

Good post by Jeff Masters on the same subject. If you scroll down to the global temperature anomaly maps for December in El Nino years 1957 and 2006 you can see a striking illustration of why this year is different. ’57 has a cold Arctic above the warm US. ’06 has a warm Arctic above a warm ’06. Compare ’06 with model projections. Compelling, I would say.

And look at Svalbard. What’s that station doing this year?

Masters also uses the same dice-rolling analogy, but I think Mike got there first…

RE: #59, Googling “Hank Roberts”+ AGW+ believer, is also instructive.
As to the language, yes, I do assume there are many who “promote” or encourage the AGW hypothesis and it’s spread, are there some who deny that? I don’t think scientists should talk like reporters no matter who you are talking to, the piece on the NBC Nightly News last night was a case in point. Again, the public hears our words and listens with their experience and vocabulary, when our precise meaning is misunderstood, perhaps intentionally so, we do no good. And I think all the talk of this issue of a warmer winter is a little strange, it has been shown that colder weather kills many more people than heat waves and is more dangerous for longer periods and exacerbates disease as well. Are you all really advocating for colder weather?

Just a short report on winter weather in Europe:
Indeed, the whole Europe is experiencing very warm winter (if a record one will be clear after it will finish), at least the start of the winter. For the first time, we were able to drive BY CAR to our cottage in High Tatras, in Slovakia in January. But there is almost NO SNOW in all the Europe. Acually, TODAY, on my way by bus from Slovakia to Netherlands, it looked like a spring trip across Europe with no signs of snow anywhere, and temperatures reaching as much as 16C.
Indeed, not a single weather event can be blamed on “global warming”, but also not a single weather event “is NOT affected by global warming”. Similarily, not a single cigatarette You will blame for cancer, but EACH cigarette contributes to the cancer… or not?

Here in Australia, we’ve just experienced the 6th warmest year on record (0.47oC above standard 1961-1990 base period), including the warmest spring on record and extremely high temperatures in the country’s west. However, average temps were pushed down by an extreme drought in the South East and South West, and a very active tropical wet season.

We’ve also experienced a near unprecedented drought, caused by the formation of the El Nino. This has devestated agriculture.

So it’s not just the US and Europe. Spare a thought for us in the South!

If anyone is interested, the 2007 Australian climate report is linked below

Dr J, you wrote “it has been shown that colder weather kills many more people than heat waves and is more dangerous for longer periods and exacerbates disease as well.”

That’s a pretty bold statement given the tens of thousands who died in recent heat waves, and the tropical diseases such as West Nile Virus that are expanding into temperate areas where they were previously unknown. Please provide the citations to support your statement or have the integrity to retract it.

The more I read about how global warming is discussed by “media / the man in the street”, the more I think that many of the questions asked about it are the problem – they are fundamentally unscientific.

People who frame questions in the manner of “Is this current hot weather due to global warming?”,

a) do not understand risk, and/or
b) do not understand that events can have multiple causes

re: 73. “I do assume there are many who “promote” or encourage the AGW hypothesis and it’s spread…”

That would be a very poor assumption as there are no legitimate (i.e., not political hacks/blogs and fiction writers) references which provide any evidence to support such a claim. To simply believe it for no good reason is to really deny science. And we are not in the Middle Ages anymore. If you are looking for promoting disinformation, just read the latest news about Exxon/Mobil’s funding of contrarians.

re #33 Although there are scientific indications that tobacco, etc directly cause some deaths and clearly aggrevate serious health problems, the professed numbers, taken as gospel from the Mount, are Jon Lovitt style hyperbole and grow as fast and add health anamolies just as fast as the populace will accept. Statistics, in the scientific and meaningful mathematical sense, they ain’t. Though nobody much cares.

a minor question: though it is probably implied, when the posts talk of El Nino “warming the pacific ocean” do they really mean the Eastern Pacific ocean which warms at the expense of the western Pacific ocean cooling. Does this make any difference ala global temperatures?

[Response: The surface warming takes place over much of the eastern and central tropical Pacific, and does not come at the expense of any surface cooling elsewhere, i.e. it is isn’t a zero sum game. Rather, the warmer SSTs are due to the breakdown of the tropical easterlies or “trade winds” in the region, which are typically responsible for the upwelling of cold deeper sub-surface water in the eastern and central tropical Pacific. In the absence of the upwelling, the surface waters are free to warm in response to solar heating. So there is a net warming of the tropical Pacific ocean surface during an El Nino event. As the tropical Pacific ocean covers a sizeable chunk of the earth’s surface, this warming is responsible for a substantial part of the projection that El Nino has on to global mean surface temperature (the warming and cooling that occurs over various regions of the extratropics in response to El Nino, by contrast, largely cancels). You can find some useful resources on El Nino on the web here at this UCAR site, on Wikipedia’s El Nino page, or on NOAA’s El Nino page. Oh, and as usual, our glossary is often a good place to look too. -mike]

Re “If the analysis was scientific as opposed to political, other factors would be considered and discusssed. For example solar (Note the current solar activity is very, very, unusual). See the attached paper that shows there is a significant correlation of average planetary temperature and the solar index-ak.”

Sure, because they scanned about 20 or 30 solar indices to find one that seemed to fit. This is called “the fallacy of the enumeration of favorable circumstances,” or to put it a shorter way, “cherry-picking.”

The only obvious physical way for the Sun to link to climate is through the Solar constant, and that has been pretty flat for the last 50 years.

I must admit I am, by some minor standards I go by, a bit happy to a few people begin to understand what NOAA’s NWS has been not doing to see to it that the public understands the truth about what’s really happening to our weather and climate.

The attribution of motive is known as the fallacy of argumentation ad hominem. I deny the motives you attribute are correct, but it doesn’t matter a bit whether they’re correct or not. One side’s motives has nothing to do with whether their argument is correct or not. A kid might be arguing that the French Revolution was in 1789 because he wants to show up his sister who guessed at 1750. But he’d still be right.

Re: 73 “I think all the talk of this issue of a warmer winter is a little strange, it has been shown that colder weather kills many more people than heat waves and is more dangerous for longer periods and exacerbates disease as well. Are you all really advocating for colder weather?”

No, I think those of us that are advocating are doing so for stability. The stable climate period during which human civilisation has developed is necessary for many reasons, only one of which is our species physical temperature range. We can, after all, either retreat to caves or wear furs, but we rely on the biota to provide everything we need, except minerals. So if water gets too warm or acidic we lose phytoplankton production, which is not only the base of the aquatic food chain but supplies a not inconsequential portion of the oxygen we need. Mention has already been made of food production in an uncertain climate. This can be affected by storms, surges of sea water, drought and pests and disease. Winter cold has a cleansing effect on some of the nasties we, as a species, have to contend with. “Normal” weather patterns are what our agricultural systems have adapted to. Can we adapt fast enough to extreme weather events at the rate they appear to be happening, and at what cost?

Re: #57
I’ve made a graph using the raw data for KNMI station The Bilt, The Netherlands. The daily data starting 1901 can be found here.
The KNMI calculates ‘normals’ every 10 years; in the graph I did it for every year; each bar represents the mean of 30 years mean temperatures ending in the year on the X-axis.
Note that there is a urban effect for The Bilt, because it is situated near the city of Utrecht. There is an estimate from the KNMI that this urban effect results in 0,2Â°C extra warming over the last century.

#51 50 years ? Strange. On all sunspot number reconstructions, cycle 19, 20, 21, 22 and 23 have not exactly the same maxima. More important, “solar constant” is no more significant, you should speak about total and spectral irradiance. For example, UV effect on stratosphere (and climate) are not presently integrated in GCM as a TOA forcing. But these UV do have an influence on climate and are studied by photochemistry and physics models. If a solar forcing is considered for 1750-2000, you should probably add this effect. As you should consider it for weather analysis, notably planetary waves, jet-stream and polar vortex. Nevertheless, It’s clear that total irradiance did not have much effect between cycles 21, 22 and 23 (less clear for 20 to 21 transition).

I think the role of el nino in mid-latitude temperature and precipitation anomalies is way overplayed. For instance, just because the current US temperature anomalies look like El Nino, doesn’t mean El Nino does a good job of explaining the anomalies.

We are currently in a 1 standard deviation El Nino event. Therefore, take the composite El Nino temperature anomaly (which is probably fairly close to a one standard deviation composite) multiply by one standard deviation and you get expected anomalies over the midwest of order of 1C. Subtract this expectation from the observed anomaly from this winter and you still have of order 10F unexplained temperature anomaly.

Even though this temperature anomaly looks like El Nino, the El Nino index only explains something like 25% of the variance. I’ve heard from folks who are well versed in El Nino dynamics, that you can only explain about 30% of the mid-latitude variance with the El Nino index. That leaves a lot of variance to other factors and I think the couple of months of data available from this year are no different.

It might be said, that this winter thusfar is quite different all around the Northern hemisphere than the previous ones. I have the foggest idea, what’s going on down there in the other side of Equator.

However, I wonder if it happened to be a case that some drastic changes to the average temperature of the climate do occur by the thus far unknown mechanism, how fast such anomalous changes can be detected by the experimental measurements?

…The atmosphere has warmed by more than seven tenths of a degree Fahrenheit (0.71 degrees F) in the past 28 years, with the bulk of that warming in the Northern Hemisphere, according to data released today by Dr. John Christy, director of the Earth System Science Center at The University of Alabama in Huntsville (UAH).

The 28-year data from Dec. 1, 1978 through Nov. 30, 2006 also show Earth’s polar extremes are heading in opposite directions: The Arctic has warmed by an average of more than two and a quarter degrees Fahrenheit (+2.27 degrees F or +1.26 C) in less than 30 years, while the Antarctic region has cooled by an average of more than half a degree (-0.55 F or -0.31 C).

The contiguous 48-states of the U.S. have warmed at an average rate of 0.29 C per decade, a change of 0.81 C or 1.46 degrees Fahrenheit in 28 years.

…The University of Alabama in Huntsville (UAH) and NOAA, Christy and Dr. Roy Spencer, a principal research scientist in the ESSC, use data gathered by microwave sounding units on NOAA satellites to get accurate temperature readings for almost all regions of the Earth.

What is the 95% confidence interval of annual average temperature estimate for the U.S. in 2006? That information is not in the NCDC press release. Kind of hard to tell if a 0.07 deg difference is significant or not without the confidence interval.

[Response: Good point, unfortunately the estimates often come without error bounds. Perhaps the error estimates (accounting for sampling uncertainties and estimate of potential systematic bias) shown for the global land surface temperature series in this figure (see part ‘b’) from chapter 2 of IPCC(2001) will give you at least a rough feel for what the uncertainties are. -mike]

Granted, year to year you can get a large range of surface temperature deviation naturally. The point I was sharing with Steve was the range in a short period (covering around 15 days and a separation of 120 miles, as a crow flies) during a season that appears to track similar to the current winter pattern. As to your measures, have you tried graphing 150 years of Christmas Eves in Chicago and reviewed the long term trend?

Re #51 and the response: The Guardian quotes climatologist David Viner as suggesting that we are not just seeing the effects of AGW, but that we may be seeing a path at the upper end of the IPCC forecast:What’s happened to winter?

Is Viner’s view an isolated one? Are other climatologists considering this, but perhaps only in the “raised eyebrows” stage?

For a follow up, my concern in the trend is not necessarily the trend of the peaks or the valleys. My concern is the trend of the differences. The greater the influence of global warming the more likely a reduction in the daily temperature range for a given weather pattern.

Please don’t assume I’m an AGW heretic, I’m here to learn from very broad knowledge base provided by this site. I am a farmer in Australia and as such GW has important implications. Warmer nights here in conjunction with less humidity (in our near desert climate the heat should radiate away quicker) suggest GW is real.
What I don’t understand is why, if water vapour is a significant GHG (the most significant according to a post I read on this site), that the tropical temperatures remain reasonably moderate despite the amount of moisture, say mid 30’s compared to experiencing 40’s in more southern(in my case) drier latitudes. Is the heat leaving the tropics on convection only.
I guess my question really is do the increasing GHG’s of all decriptions act only as a trap for heat radiation or can they actually insulate against some of it.

Re Magnus W , replying to your first comment (sorry I’m so late), ESRL’s Monthly/Seasonal Climate Composites site allows you to create national or global graphs showing the difference between two arbitrary periods (between 1948 and 2006). This lets you show the anomaly versus an arbitrary baseline. For example, select ‘Air Temperature’ in the ‘Which variable’ box, ‘Surface’ in the ‘Level’ box, jan for the beginning month, dec for the ending month, 2006 to 2006 in the ‘Enter Range of Years’ boxes, 1948 to 1977 in the ‘optional minus’ boxes, and you should see a graph of global temp anomalies versus a 1948 to 1977 baseline. It shows most of the earth with about 0.5 C – 1C of warming, with a few cool patches around Australia, south of Alaska, and west of the tip of South America. Most of the Arctic is at least 3C warmer, and ranges up to 7C warmer near Svalbard. Some similar ERSL sites can be found via the CDC Interactive Plotting and Analysis Pages.

What I don’t understand is why, if water vapour is a significant GHG (the most significant according to a post I read on this site), that the tropical temperatures remain reasonably moderate despite the amount of moisture, say mid 30’s compared to experiencing 40’s in more southern(in my case) drier latitudes. Is the heat leaving the tropics on convection only.

Most of the large land masses are away from the equator – which means much of the solar radiation intercepted by the tropics warms the ocean. Water can absorb much more heat than air. This moderates the temperatures of the tropics. In addition – moist air is less dense, and will rise faster than dry air at the same temperature. So moist air transports heat into the upper troposphere much faster than dry air. This moderates surface temperatures, a property which is largely independent of water vapor’s GHG properties (which are due to its optical properties).